This is 'A Will To Murder' by Hilary Thomson.
"When wealthy and eccentric patriarch James Boyle dies a peculiardeath, the DA declines to investigate, convinced that the victim diedof natural causes. Yet even the police are stunned when members of theBoyle family gather at the estate of Rollingwood for the reading ofJames' will--and begin to die, one at a time. Only when long-lostrelative Bradley Smith appears, along with reporter Eric Maxwell, dothe mysterious deaths finally receive a proper investigation. Even so,no one is prepared for the lunacy that hides beneath the mansion'sbizarre facade."
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Doesn't that sounds good?